FDA OKs using viruses to fight Listeria in meat

Aug 22, 2006 (CIDRAP News) – US health officials broke new ground last week by approving the use of a mixture of bacteriophages, or bacteria-killing viruses, to control the pathogen Listeria monocytogenes on ready-to-eat (RTE) meat and poultry products.

The Food and Drug Administration (FDA) concluded that a mixture of six bacteriophages developed by Intralytix, Inc., Baltimore, is safe to use. The product, called LMP 102, is the first bacteriophage preparation approved for use as a food additive.

The product is intended to be sprayed on RTE meats such as sliced ham and turkey. Each of the bacteriophages in it targets various L monocytogenes strains, and the use of six different phages is intended to reduce the risk that Listeria would develop resistance, according to the FDA record of its decision on the product.

Phages infect only bacteria and are part of the normal microbial population of the human intestinal tract, according to the FDA. L monocytogenes can grow at refrigerator temperatures and can cause serious illness, particularly in pregnant women, newborns, and people with weak immunity.

The phages in LMP 102 are grown in Listeria cultures, the FDA said. In examining the product's safety, the agency looked at whether it contains any potentially harmful Listeria residues, particularly one called Listeriolysin O (LLO). Investigators did not detect LLO in the product, and mechanisms in the gut would be likely to inactivate any trace amount present.

The report also says that some phages can serve to transfer toxin or drug-resistance genes between bacterial cells, but the phages used in LMP 102 are not that kind.

The FDA document does not say exactly how effective the product is in reducing Listeria on RTE meats. But John Vazzana, president and CEO of Intralytix, said that in company tests, LMP 102 has reduced Listeria by 99% to 99.9% (2 to 3 logs) on foods with relatively high levels of contamination.

"We concluded from those tests that we could basically get rid of 99% of any LM [L monocytogenes] that's present," Vazzana told CIDRAP News.

He said Intralytix has licensed the product to a multinational company that serves the food processing industry, but declined to name it. "I would think we're probably 6 months away from the product being used commercially," he said.

The FDA said its action signals only that the product meets the safety standards of the Federal Food, Drug, and Cosmetic Act. The product must also comply with meat and poultry inspection laws that are administered by the US Department of Agriculture (USDA), which require that food additives be "suitable" for their intended use, the agency said.

Vazzana said the USDA has been "actively involved" in the FDA review of LMP 102 and that USDA approval is not in doubt. "This is not new to them; they've reviewed the petition, they've approved the product," he said.

The USDA will be developing guidelines for use of the product, "and that's a process we'll be going through over the next several weeks," he added.

Vazzana said the product may have to be listed on food labels, depending on what the USDA decides. He said that shouldn't scare consumers, given that phages are "the most ubiquitious organisms on the planet today."

"I think what we have to communicate to the consumer is that this is an all-natural approach" and that it will affect only Listeria, he said. "We believe this is a much better solution to a serious problem than using hordes of chemicals."

Vazzana estimated that using LMP 102 will add less than a penny a pound to the cost of RTE meat and poultry products.

Food safety expert Craig Hedberg, PhD, said he agreed with the FDA that LMP 102 is likely to be safe, but he was cautious in assessing its likely contribution to controlling Listeria. Hedberg is an associate professor of environmental and occupational health at the University of Minnesota School of Public Health in Minneapolis.

"Theoretically, phages make a nice control measure, but the real-world application of these products almost always falls short of the ideal situation," he told CIDRAP News by e-mail.

"This seems to be another tool in the toolkit to control Listeria," he added. "As such, it gives producers a greater range of options on control. The key to Listeria control is the successful integration of the various tools and careful monitoring of the systems to make sure everything is working as it should."